Conventionally, in some image forming apparatuses such as color printers of an electrophotographic system, other than process color developers constituting a print image of cyan (hereinafter also referred to as “C”), magenta (hereinafter also referred to as “M”), yellow (hereinafter also referred to as “Y”), black (hereinafter also referred to as “K”), etc., a white (hereinafter also referred to as “W”) developer is used with the aim to shield the base color of the print medium (for example, see Patent Document 1). In the invention, “black color information” means color information corresponding to black that is one of the process color developers. For example, when there are four process color developers, C, M, Y and K, color information regarding the K (which includes a value of 0% to 100%) is used for the information.